In recent years, steam turbines have been often started up by a method called optimal startup. In the optimal startup, a steam turbine is started up by successively predicting a steam temperature, a steam pressure, a heat transfer coefficient and the like of the steam turbine and controlling startup operation such that the rate of speed increase or the rate of load increase in the steam turbine reaches a maximum within a range in which a thermal stress of a turbine rotor does not become excessively high.
In addition, studies have been conducted on a method of predicting the time taken for the startup of the steam turbine in the application of the optimal startup (startup time). However, it is difficult to predict the startup time in the application of the optimal startup with high accuracy, and applying the prediction result of the startup time to an actual steam turbine (an actual machine) presents challenges. For an operating party of a power plant, the prediction of the startup time with high accuracy has an advantage of accurately responding a power demand request, and an advantage of reducing the operational cost of the power plant. For this reason, there are great demands of the operating party for the prediction of the startup time.